PB2505: THERAPEUTIC PHLEBOTOMY INSTANTLY AFFECTS BLOOD PARAMETERS AND VISCOCITY IN SICKLE CELL DISEASE PATIENTS
Authors: Amna Jebali, Yanis Pelinski, Nassim Ait Abdallah, Habibi Anoosha, Phillipe Connes, Pablo Bartolucci
Journal: HemaSphere (2023)

Topic: 26. Sickle cell disease Background: Sickle cell disease (SCD) is the most common genetic disease worldwide. It is characterized by a single mutation in the hemoglobin gene (HbS), which causes HbS molecules to form aggregates and polymerize. SCD RBCs have a distinct “sickle” shape, are rigid and do not easily flow through the microcirculation, causing frequent vaso-occlusive crises (VOC) in affected patients. Due to the heterozygocity of the HbS gene, clinically milder forms of the disease exist, such as hemoglobin SC disease (SC), where HbS coexists with HbC. This leads to the crystallization of HbC, which promotes RBC dehydration, resulting in an increase of Hb concentration, HbS polymerization and loss of RBD deformability. Due to their higher Hb concentrations, SC patients are usually less anemic and experience fewer VOC than homozygous SS patients. Therapeutic phlebotomy is a technique commonly used to reduce blood hyperviscocity (Hb>11.5 g/dl) in SC patients, and which is also used in SS patients suffering from severe and repeated VOC crises in hopes of reducing HbS concentration when Hb 9.5<g/dL. Aims: The aim of this project was to evaluate the immediate impacts of therapeutic phlebotomy on blood parameters and blood viscocity. Methods: Over a 7-month period, blood samples from SS and SC patients, as well as AA controls, were collected just before and within one hour after therapeutic phlebotomy. Blood parameters were analyzed and blood viscocity was measured after full oxygenation of the blood, at native hematocrit, room temperature, and a shear rate of 225 s-1 using a cone/plate viscometer. Results: Blood samples from 29 patients were analyzed, of which 10 had the SS genotype, 10 had the SC genotype, and 9 were AA controls who received therapeutic phlebotomy for hemochromatosis (n=7) or hyperferritinemia (n=2). Female to male ratio was 0.25, 0.67, and 0.8 in each group, and mean age was 42 (±3), 43 (±4), and 55 (±3) years of age respectively. Analysis showed that following phlebotomy, hemoglobin was significantly decreased (P ≤ 0.01) in all patients, regardless of their genotype. Hematocrit concentration also decreased (P ≤ 0.01) in SS and AA patients, although the effect was stronger in SC patients (P ≤ 0.001). Surprisingly, within one hour of therapeutic phlebotomy, there was already a significant decrease in blood viscocity (P ≤ 0.01) across all patients regardless of genotype. We therefore calculated the hematocrit-to-viscocity (HTV) ratio, which reflects a balance between blood oxygen carrying capacity (i.e., hematocrit) and blood flow resistance (i.e., blood viscosity): the highest the HTV, the greatest the RBC oxygen transport effectiveness. Following phlebotomy, the HTV ratio significantly increased in the SS and AA groups (P ≤ 0.01 and P ≤ 0.05 respectively), however it was not the case for SC patients. Summary/Conclusion: Our results show for the first time that therapeutic phlebotomy has a direct and immediate impact on blood parameters and hemorrheology. It is now necessary to understand the physiology behind viscosity and HTV ratio changes following phlebotomy, and whether these changes are related to renal involvement and sustained over 48h. Keywords: Red blood cell, Sickle cell disease